Method and Apparatus for Improving Radio Frequency Identification Coverage

ABSTRACT

A method and apparatus are disclosed for improving RFID coverage using an antenna array having an adaptive antenna beam. The apparatus includes an RFID reader including an antenna array having a plurality of antenna elements. Subsets of the plurality of antenna elements are selectively activating in order to direct an antenna beam to communicate with at least one RFID tag. The method includes transmitting an interrogation signal from an antenna array by activating one or more subsets of a plurality of antenna elements forming the antenna array. In this way, the interrogation signal is directed thereby improving antenna coverage.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/628,211, filed on Jun. 20, 2017, which is a continuation of U.S.patent application Ser. No. 13/329,438, filed on Dec. 19, 2011, both ofwhich are incorporated herein by reference in their entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to antenna arrays, and moreparticularly to antenna arrays having an adaptive (steerable) antennabeam that may be employed to improve coverage in a radio frequencyidentification (RFID) system.

BACKGROUND

RFID technology allows identification data to be collected remotely,which provides a significant advantage in identifying articles, parcelsor other items. To access identification data stored in an RFIDtransponder (commonly referred to as a “RFID tag” or “tag”), an RFIDreader/encoder generates an energy field via a transmission beam tointerrogate the RFID tag, and subsequently, to retrieve data stored inthe RFID tag. The data received from the RFID tag is processed by acomputer system to identify the item that is associated with the RFIDtag. Due to its convenience and reliability, RFID technology has found awide range of applications, including item tracking, item location,inventory assessment, etc.

However, complications may occur in the detection of RFID tags inmonitored areas where the dimensions of the monitored area present RFIDcoverage challenges. To attempt to overcome these challenges,conventional RFID reader systems employ multiple RFID readers placedabout the monitored area. Nevertheless, detection challenges persist dueto the fixed transmission beams of the stationary RFID readers and tomultipath which causes fluctuations and areas of weak signal strength inthe monitored area. Moreover, if the items are randomly placed andoriented within the monitored area, the RFID tags (and the respectiveantennas) will be randomly oriented with respect to the fixed RFIDreaders. Random orientation may result in a weak responsive signal fromthe RFID tag and also promote polarization errors and other deficienciesin the signals returned from the RFID tag(s).

BRIEF DESCRIPTION OF THE FIGURES

The accompanying figures, where like reference numerals refer toidentical or functionally similar elements throughout the separateviews, together with the detailed description below, are incorporated inand form part of the specification, and serve to further illustrateembodiments of concepts that include the claimed invention, and explainvarious principles and advantages of those embodiments.

FIG. 1 is a block diagram of an antenna array having an adaptive antennabeam and a plurality of items having RFID tags in accordance with someembodiments.

FIG. 2 is a top plan view of a monitored area in accordance with someembodiments.

FIG. 3 is a top plan view of the monitored area of FIG. 2 illustratingthe RFID coverage from a plurality of ceiling mounted RFID readers inaccordance with some embodiments.

FIG. 4 is a functional block diagram of an RFID reader in accordancewith some embodiments.

FIGS. 5-13 are illustrations of various antenna array configurations inaccordance with some embodiments.

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale. For example, the dimensions of some of the elements inthe figures may be exaggerated relative to other elements to help toimprove understanding of embodiments of the present invention.

The apparatus and method components have been represented whereappropriate by conventional symbols in the drawings, showing only thosespecific details that are pertinent to understanding the embodiments ofthe present invention so as not to obscure the disclosure with detailsthat will be readily apparent to those of ordinary skill in the arthaving the benefit of the description herein.

DETAILED DESCRIPTION

Techniques are disclosed for improving RFID coverage using an antennaarray having an adaptive antenna beam. An RFID reader includes anantenna array having a plurality of antenna elements that may beselectively activated in one or more subsets in order to direct anantenna beam to communicate with at least one RFID tag. In this way, theproperties of the transmitted signal are changed whereby coverage isimproved in monitored areas that are subject to multipath propagationeffects.

FIG. 1 is a block diagram of an antenna array 100 having an adaptiveantenna beam 102 a-102 d and a plurality of items 106, each item 106having an RFID tag 108 fixed or otherwise associated thereto. It will beappreciated that while four antenna beams 102 a-102 d are illustrated inFIG. 1, that any number of antenna beams may be formed depending uponthe size of the array and the number and location of activated antennaelements. In accordance with various embodiments of the presentdisclosure, each of the RFID tags 108 may be either an active tag, i.e.,a tag which has a self contained power supply or, as is more usually thecase, may be a passive tag that requires external excitation when it isto be read or interrogated within a monitored area of an RFID reader110. In one implementation, the RFID reader 110 includes the antennaarray 100, one or more transmit/receive (T/R) modules 112 and a beamforming processor 114, which in some embodiments may be realized as adigital signal processor (DSP) 114. In a multi-reader implementation,each RFID reader 110 communicates with a system controller (not shown inFIG. 1) via a link or bus 116. As illustrated in FIG. 1, the antennaarray 100 of the RFID reader 110 has an adaptive (or steerable) antennabeam 102 a-102 d. This allows the transmit power or focus of thereceiver to be directed toward a particular area within the monitoredarea to interrogate one or more RFID tags 108. Again, although FIG. 1illustrates four distinct antenna beams 102 a-102 d, it will beappreciated that many more antenna beams may be utilized in anyparticular implementation of the antenna array 100.

FIG. 2 is a top plan view of a monitored area 200 in accordance withsome embodiments. Within the monitored area 200, several RFID readers110 with their respective antenna arrays 100 may be positioned toprovide adequate coverage to be able to interrogate RFID tags anywherewithin the monitored area 200, such as, for example, on shelving 202.Generally, the RFID readers 110 (with their respective antenna arrays100) may be positioned anywhere within the monitored area, includingwithout limitation, on a shelving unit 202′, on a wall 204, on a supportpost 206 or configured on the ceiling (which is transparent in FIG. 2)of the monitored area 200.

FIG. 3 is a top plan view of the monitored area 200 of FIG. 2illustrating the RFID coverage from a plurality of ceiling mounted RFIDreaders 110 in accordance with some embodiments. As can be seen, eachRFID reader 110 has a coverage area 300 within which an antenna beam maybe directed (see FIG. 1) to interrogate and receive responsive signalsfrom one or more RFID tags (not shown in FIG. 3). Typically, thecoverage areas 300 overlap to some extent, which presents options forinterrogating the RFID tags from one or more RFID readers 110. In thisway, the overlapping RFID coverage area and adaptable antenna beamsafford the RFID system of the present disclosure a more efficient andreliable opportunity to read the RFID tags within the monitored area200.

FIG. 4 is a functional block diagram of an RFID reader 110 in accordancewith some embodiments. As noted above, the RFID reader 110 includes theantenna array 100 that includes a number of antenna elements 400configured in some array pattern. In the illustrated embodiment, eachantenna element 400 is coupled to a respective T/R module 112, which inturn, is coupled to a beam forming processor 114, which may be a DSP.For other embodiments, it will be appreciated that the T/R modules neednot have a one-to-one correspondence to the number of antenna elements.Each RFID reader 110 communicates (in a multi-reader system environment)via bus 116 with a system controller 402, which may direct anyparticular RFID reader to transmit an interrogation signal to one ormore RFID tags and receive a responsive signal from the RFID tag. Thatis, a single RFID reader 110 may be instructed by the controller 402 totransmit a signal to and receive a signal from an RFID tag, or one ormore RFID readers 110 may receive commands from the controller 402 totransmit a signal to and receive a signal from the same RFID tag(s).

FIG. 5 is an illustration of an antenna array 100 in accordance withsome embodiments. The illustrated antenna array 100 includes nineantenna elements 500 arranged in a 3×3 array, however, it will beappreciated that any array configuration may be employed following theteachings of the present disclosure. The antenna elements may berealized in any of a number of antenna types (e.g., loop, dipole,monopole, patch or helix), and FIG. 5 presents the antenna elements aspatch antennas. As will be appreciated, patch antennas may be driven(activated) in a vertical polarization, horizontal polarization orcircular polarization. Also, a patch antenna may be realized as adual-port (or dual element) antenna element that may be activated in ahorizontal or vertical polarization (for example) depending upon theactivation source.

According to various embodiments of the present disclosure, varioussubsets of the antenna elements 500 of the antenna array 100 areactivated to direct (or steer) the antenna beam of the antenna array 100within the coverage area (300 in FIG. 3). In the example illustrated inFIG. 5, a first subset 502 may be utilized forming a squareconfiguration to transmit an interrogation signal to an RFID tag andthen to receive the responsive signal. It will be appreciated thatwireless communication is often impaired by the nature of the coveragearea. One example is the impairment caused by the multiple paths that RFsignals travel between the RFID reader and tag antenna. Often themultiple paths create destructive interference, causing the poor signalstrength over portions of the coverage area in areas that wouldordinarily be within range (as determined by the transmit power,distance between antennas, reader antenna gain, and tag antenna gain).By varying the selection of antenna element subsets, the antenna beamtransmission properties (e.g., gain) will vary. Accordingly, should theresponsive signal from the RFID tag have poor signal strength or qualityusing all antenna elements of the antenna array 100, a subset of antennaelements may be employed to transmit the interrogation signal and/orreceive the responsive signal from the RFID tag, which may yield aresponsive signal from the RFID tag having a better signal strength orquality. Since the beam centers are the geographic centers of theactivated antenna elements 500, the various antenna beams will also beshifted in phase. In this manner of selecting the full set of antennaelements or subsets of antenna elements, the transmission propertieswill change due to the varying gain and beam centers, and thedestructive effects of multipath propogation are reduced or eliminated.Alternately, the first subset 502 may be used to transmit aninterrogation signal to the RFID tag, and the second subset 504 may beemployed to receive the responsive signal from the RFID tag. The varietyof possible subsets together with the polarization options noted above,offers a myriad of antenna beam and polarization combinations providinga versatile approach to interrogating and reading RFID tags within amonitored area (200 of FIG. 3).

FIG. 6 is another illustration of an antenna array 100 in accordancewith some embodiments. As shown in FIG. 6, a first subset 602 of sixantenna elements 600 in a rectangular array may be used for transmissionand/or reception. Using this subset provides a beam center 606 and anantenna beam with properties that differ from the beam formed using thefull set of antenna elements or other subset of antenna elements.Additionally or alternately, a second subset 604 may be used (providingbeam center 608). It will be appreciated that in FIG. 6, all of theantenna elements are collectively activated between the subsets 602 and604, while in FIG. 5, some antenna elements 500′ were not activated forthe exemplary transmission/reception session. Alternately, the antennaelements 600 of FIG. 6 could be arranged as three subsets of 1×3rectangular arrays (arranged vertically or horizontally), which wouldproduce a beam center at the center of the middle subset antenna elementand transmission properties commensurate with a 1×3 geometry.

Referring now to FIGS. 7 and 8, an exemplary array of dipole antennaelements are shown. In FIG. 7, the dipole antenna elements 700 arehorizontally polarized, while in FIG. 8 the dipole antenna elements 800are vertically polarized. It will be appreciated that dipole antennaelements 700 and 800 could be mixed into a combined array, if desired,for any particular implementation. In the exemplary embodiment of FIG.7, a first subset 702 of the horizontally polarized dipole antennaelements 700 are configured in a horizontal rectangular configurationhaving an antenna beam center 704 in the center of the subset 702.Another subset 706 could also be activated to provide a verticalrectangular configuration of the horizontally polarized dipole antennaelements 700. This subset would shift the beam center as indicated by708. As noted above, in some transmission and/or reception sessions, notall of the antenna elements 700′ need to be activated.

FIG. 8 illustrates that the subsets 802 and 806 of the verticallypolarized dipole antenna elements 800 need not have a commonconfiguration. The subset 802 has a square structure with a beam center804, while the subset 806 has a vertically oriented rectangularconfiguration with a beam center 808. It will be appreciated that inlarger array sizes (e.g., 5×5, 8×8) the activated antenna elements 800may form array subsets in manifold ways.

Referring now to FIG. 9, still more subset combination variations ofantenna element 900 are illustrated. As can be seen, three helicalantenna elements 900 are activated to form a horizontal 1×3 rectangularsubset 902 with a beam center, 904. For a subsequent transmission and/orreception session, subset 906 may be employed, which forms a verticallyarranged rectangular subset of helical antenna elements 900 having abeam center at 908.

FIG. 10 illustrates the possibility of activating all of the loopantenna elements 1000 as a superset 1002 having a beam center at 1008.In prior or subsequent transmission and/or receptions sessions, 1×3subsets 1004 and/or 1006 may be used to direct (steer) the beam centerbetween 1010 and 1012, as desired, to communicate with one or more RFIDtags (108 in FIG. 1).

FIG. 11 illustrates still further exemplary embodiments provided in ahexagonal array 1100 formed of monopole antenna elements 1102. A firstsubset 1104 having a beam center 1106 is configured in a triangulararrangement. A second subset 1108 also has a triangular configuration,but is inverted relative to the first subset 1104, and has a beam center1110. Again, it will be appreciated that many and varied combinations ofantenna elements 1102 may be activated to form a plethora of subsets.

FIG. 12 expands upon FIG. 11 by illustrating a dual-hexagonal array 1200that includes a hexagonal array of antenna elements 1202 (e.g., monopoleelements) having a first polarization (e.g., vertical). Also, a secondhexagonal array of antenna elements 1204 (e.g., loop elements) having asecond polarization (e.g., horizontal) is positioned interleaved withinthe hexagonal array of antenna elements 1202. Due to the differentpolarizations, the hexagonal arrays do not interfere with the operationof each other and may be configured as illustrated in FIG. 12 or in amultitude of other arrangements as will be appreciated. In someembodiments, the subsets of the dual-hexagonal array 1200 may be formedas all of the antenna elements 1202 and all of the antenna elements1204. In other embodiments, a subset 1206 of the antenna elements 1202may form one subset, while a subset 1208 of the antenna elements 1204may form another subset. In still further embodiments, one subset couldbe formed by all of the antenna elements 1202, while a second subset1208 of the antenna elements 1204 may form another subset.

By now it will be appreciated that myriad of antenna elements types maybe selectively activated to form a multitude of subsets affording theadvantage of directing (steering) an antenna array beam with varyingtransmission properties and phase shifting the beam center. FIG. 13illustrates yet another possible implementation of a dual circular array1300 having subsets formed of antenna elements 1302 and 1304. In asuperset configuration, all of the antenna elements 1302 and 1304 couldbe activated. Additionally or alternately, dual circular subsets couldbe formed by individually activating the antenna elements 1302 for onetransmission and/or reception session, while activating the antennaelements 1304 for another transmission and/or reception session.

Accordingly, techniques have been disclosed for improving RFID coverageusing an antenna array having an adaptive antenna beam. The antenna beamis adapted about a monitored area by selectively activating varioussubsets of antenna elements. The subsets may be configured in manifoldways and provide an antenna beam with changing transmission propertiesand shifted beam center, and may include a polarization change betweenselection of the activated antenna element subsets. Naturally, thesuperset of all of the antenna elements may be employed, if desired, inany particular implementation of the teachings provided by the presentdisclosure.

In the foregoing specification, specific embodiments have beendescribed. However, one of ordinary skill in the art appreciates thatvarious modifications and changes can be made without departing from thescope of the invention as set forth in the claims below. Accordingly,the specification and figures are to be regarded in an illustrativerather than a restrictive sense, and all such modifications are intendedto be included within the scope of present teachings.

The benefits, advantages, solutions to problems, and any element(s) thatmay cause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as critical, required, or essentialfeatures or elements of any or all the claims. The invention is definedsolely by the appended claims including any amendments made during thependency of this application and all equivalents of those claims asissued.

Moreover in this document, relational terms such as first and second,top and bottom, and the like may be used solely to distinguish oneentity or action from another entity or action without necessarilyrequiring or implying any actual such relationship or order between suchentities or actions. The terms “comprises,” “comprising,” “has”,“having,” “includes”, “including,” “contains”, “containing” or any othervariation thereof, are intended to cover a non-exclusive inclusion, suchthat a process, method, article, or apparatus that comprises, has,includes, contains a list of elements does not include only thoseelements but may include other elements not expressly listed or inherentto such process, method, article, or apparatus. An element proceeded by“comprises . . . a”, “has . . . a”, “includes . . . a”, “contains . . .a” does not, without more constraints, preclude the existence ofadditional identical elements in the process, method, article, orapparatus that comprises, has, includes, contains the element. The terms“a” and “an” are defined as one or more unless explicitly statedotherwise herein. The terms “substantially”, “essentially”,“approximately”, “about” or any other version thereof, are defined asbeing close to as understood by one of ordinary skill in the art, and inone non-limiting embodiment the term is defined to be within 10%, inanother embodiment within 5%, in another embodiment within 1% and inanother embodiment within 0.5%. The term “coupled” as used herein isdefined as connected, although not necessarily directly and notnecessarily mechanically. A device or structure that is “configured” ina certain way is configured in at least that way, but may also beconfigured in ways that are not listed.

It will be appreciated that some embodiments may be comprised of one ormore generic or specialized processors (or “processing devices”) such asmicroprocessors, digital signal processors, customized processors andfield programmable gate arrays (FPGAs) and unique stored programinstructions (including both software and firmware) that control the oneor more processors to implement, in conjunction with certainnon-processor circuits, some, most, or all of the functions of themethod and/or apparatus described herein. Alternatively, some or allfunctions could be implemented by a state machine that has no storedprogram instructions, or in one or more application specific integratedcircuits (ASICs), in which each function or some combinations of certainof the functions are implemented as custom logic. Of course, acombination of the two approaches could be used.

Moreover, an embodiment can be implemented as a computer-readablestorage medium having computer readable code stored thereon forprogramming a computer (e.g., comprising a processor) to perform amethod as described and claimed herein. Examples of suchcomputer-readable storage mediums include, but are not limited to, ahard disk, a CD-ROM, an optical storage device, a magnetic storagedevice, a ROM (Read Only Memory), a PROM (Programmable Read OnlyMemory), an EPROM (Erasable Programmable Read Only Memory), an EEPROM(Electrically Erasable Programmable Read Only Memory) and a Flashmemory. Further, it is expected that one of ordinary skill,notwithstanding possibly significant effort and many design choicesmotivated by, for example, available time, current technology, andeconomic considerations, when guided by the concepts and principlesdisclosed herein will be readily capable of generating such softwareinstructions and programs and ICs with minimal experimentation.

The Abstract of the Disclosure is provided to allow the reader toquickly ascertain the nature of the technical disclosure. It issubmitted with the understanding that it will not be used to interpretor limit the scope or meaning of the claims. In addition, in theforegoing Detailed Description, it can be seen that various features aregrouped together in various embodiments for the purpose of streamliningthe disclosure. This method of disclosure is not to be interpreted asreflecting an intention that the claimed embodiments require morefeatures than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive subject matter lies in less than allfeatures of a single disclosed embodiment. Thus the following claims arehereby incorporated into the Detailed Description, with each claimstanding on its own as a separately claimed subject matter.

1. A radio frequency identification (RFID) reader, comprising: anantenna array including a plurality of antenna elements; atransmit/receive module coupled to the plurality of antenna elements;and a beam forming processor coupled to the transmit/receive module andconfigured to selectively activate the plurality of antenna elements ina full set of antenna elements to generate a steerable transmission beamcapable of interrogating at least one RFID tag by steering the steerabletransmission beam towards a particular area within a monitored region,wherein the beam forming processor is further configured to: activate afirst subset of antenna elements of the full set of antenna elements totransmit a first RFID interrogation signal to interrogate the at leastone RFID tag; receive, using a second subset of antenna elements of thefull set of antenna elements, a first RFID response signal from the atleast one RFID tag in response to the first RFID interrogation signal;determine a signal quality of the first RFID response signal; inresponse to determining the signal quality of the first RFID responsesignal: change the antenna elements in the second subset to a thirdsubset of antenna elements of the full set of antenna elements; andactivate the third subset of antenna elements to transmit a second RFIDinterrogation signal to again interrogate the at least one RFID tag toreceive a second RFID response signal from the at least one RFID tag. 2.The RFID reader of claim 1, wherein the plurality of antenna elementsare spaced approximately one-half wavelength apart.
 3. The RFID readerof claim 1, further comprising a controller coupled to the beam formingprocessor.
 4. The RFID reader of claim 1, wherein the beam formingprocessor selectively activates all of the plurality of antennaelements.
 5. The RFID reader of claim 1, wherein the plurality ofantenna elements comprises one or more antenna types from the followinggroup of antenna types: monopole, dipole, loop, helical and patch. 6.The RFID reader of claim 5, wherein the plurality of antenna elementsare polarized with one or more of the following group of antennapolarizations: vertical, horizontal and circular.
 7. The RFID reader ofclaim 1, wherein the first subset and the second subset have a commonpolarization for the respective transmitting and receiving.
 8. The RFIDreader of claim 1, wherein the first subset and the second subset havedifferent polarization for the respective transmitting and receiving. 9.The RFID reader of claim 1, wherein the RFID reader and at least oneother RFID reader are coupled to a controller configured to control theRFID reader and the at least one other RFID reader.
 10. A radiofrequency identification (RFID) reader, comprising: an antenna arrayincluding a plurality of antenna elements; a transmit/receive modulecoupled to the plurality of antenna elements; and a beam formingprocessor coupled to the transmit/receive module and configured toselectively activate the plurality of antenna elements in a full set ofantenna elements to generate a steerable antenna beam by steering thesteerable antenna beam towards a particular area within a monitoredregion to receive a signal from at least one RFID tag, wherein the beamforming processor is further configured to: activate a first subset ofantenna elements of the full set of antenna elements to transmit a firstRFID interrogation signal to interrogate the at least one RFID tag;receive, using a second subset of antenna elements of the full set ofantenna elements, a first RFID response signal from the at least oneRFID tag in response to the first RFID interrogation signal; determine asignal quality of the first RFID response signal; in response todetermining the signal quality of the first RFID response signal: changethe antenna elements in the second subset to a third subset of antennaelements of the full set of antenna elements; and activate the thirdsubset of antenna elements to transmit a second RFID interrogationsignal to again interrogate the at least one RFID tag to receive asecond RFID response signal from the at least one RFID tag.
 11. The RFIDreader of claim 10, wherein the plurality of antenna elements are spacedapproximately one-half wavelength apart.
 12. The RFID reader of claim10, further comprising a controller coupled to the beam formingprocessor.
 13. The RFID reader of claim 10, wherein the plurality ofantenna elements comprises one or more antenna types from the followinggroup of antenna types: monopole, dipole, loop, helical and patch. 14.The RFID reader of claim 10, wherein the RFID reader and at least oneother RFID reader are coupled to a controller configure to control theRFID reader and the at least one other RFID reader.
 15. The RFID readerof claim 10, wherein the first and second subsets have a differentpolarization.
 16. A method, comprising: activating a first subset ofantenna elements of a plurality of antenna elements forming an antennaarray to: generate a steerable antenna beam configured to transmit afirst radio frequency identification (RFID) interrogation signal fromthe first subset of antenna elements, steer the steerable antenna beamtowards a particular area within a monitored region, and interrogate atleast one RFID tag; receiving, using a second subset of antenna elementsof the plurality of antenna elements, a first RFID response signal fromthe at least one RFID tag in response to the first RFID interrogationsignal; determining a signal quality of the first RFID response signal;in response to determining the signal quality of the first RFID responsesignal: changing the antenna elements in the second subset to a thirdsubset of antenna elements of the plurality of antenna element; andactivating the third subset of antenna elements to transmit a secondRFID interrogation signal to again interrogate the at least one RFID tagto receive a second RFID response signal from the at least one RFID tag.17. The method of claim 16, further comprising receiving the second RFIDresponse signal via activating a different subset of antenna elementsthan was used to transmit the second RFID interrogation signal.